Position detection apparatus, position detection method, exposure apparatus, device manufacturing method, and substrate

ABSTRACT

An apparatus which detects a position of a target mark included in an object. The apparatus includes a unit which senses an image of the object, a unit which extracts a first mark and a feature of a region outside of the first mark in the image, and a unit which detects a position of the target mark based on a position of the first mark and the feature.

FIELD OF THE INVENTION

The present invention relates to a position detection apparatus andposition detection method, an exposure apparatus, a device manufacturingmethod, and a substrate and, more particularly, to a position detectionapparatus and position detection method which detect the position of amark on an object, an exposure apparatus including the apparatus, adevice manufacturing method using the apparatus, and a substrate adaptedto such a position detection apparatus.

BACKGROUND OF THE INVENTION

A semiconductor device is manufactured by repeating a lithography stepfor projecting and exposing a device pattern formed on a master (e.g., areticle or mask) to a substrate (e.g., a wafer or glass substrate)coated with a photosensitive material and developing the device pattern.In such a manufacturing step, it is important to accurately align adevice pattern (latent image) to be projected and exposed to aphotosensitive material to a device pattern (patterned structure)already formed on a substrate.

An example of operation for aligning the pattern of a master to apattern formed on a substrate is substrate alignment. In themanufacturing step of forming a semiconductor device on a wafer, suchsubstrate alignment is called wafer alignment.

Wafer alignment is performed in accordance with the following procedure.First, a wafer is supplied to a lithography system having an exposureapparatus and a mechanical alignment apparatus. Coarse alignment is doneby the mechanical alignment apparatus using an orientation flat or notchformed at the peripheral portion of the wafer. Then, the wafer is placedon the wafer chuck of the exposure apparatus by a wafer supplyapparatus. The typical alignment accuracy by the mechanical alignmentapparatus is about 20 μm.

Next, the positions of a plurality of alignment marks (positiondetection marks) formed on the wafer by a preceding step are detectedusing an alignment scope. The X- and Y-direction shifts and rotationcomponent of the wafer and the magnification component of the shot arrayare calculated on the basis of the detection result. In exposing eachshot, the wafer stage is driven on the basis of the calculation result.Accordingly, the pattern already formed in a shot is accurately alignedto the pattern projected onto the wafer through a projecting opticalsystem. This scheme will be called global alignment. The accuracy ofglobal alignment is 50 nm or less in an exposure apparatus formanufacturing, e.g., a 256-Mbit memory.

In recent years, a planarization technique by a polishing step calledCMP (Chemical Mechanical Polishing) is often used. When CMP is executed,the layer on the alignment mark is polished. This degrades a mark signalor decreases stability. To prevent this, an alignment mark is oftenoptimized in accordance with the process. This optimization is performedby forming a plurality of tentative alignment marks having differentstructures such as line widths, pitches, and three-dimensional patternsand selecting an optimum alignment mark. Normally, an optimum alignmentmark is determined at the time of prototype formation. In a flexiblemanufacturing system, however, mass production sometimes starts withoutexecuting optimization. In this case, a plurality of alignment marks mayenter the visual field of the alignment scope.

Additionally, in recent years, a method of forming a plurality of setsof alignment marks in one region (exposure region) is replacing a methodof forming a set of X and Y alignment marks in one region. This aims at,e.g., correcting a deformation of the exposure region or increasing themeasurement accuracy by an averaging effect obtained by measuring aplurality of alignment marks. For such purposes, the accuracy must beincreased by ensuring the span between the alignment marks is as wide aspossible. More specifically, four alignment marks are formed at the fourcorners of each exposure region. Also, with this background, a pluralityof alignment marks may enter the visual field (the field of view) of analignment scope at a high probability.

Furthermore, as the number of steps increases recently along with anincrease in complexity of a device structure, the number of times ofalignment mark formation increases.

More specifically, the number or layout density of alignment marksincreases in recent years in accordance with various purposes or factorssuch as optimization of the alignment mark structure, improvement ofmeasurement accuracy, and the increase in the number of steps.Accordingly, a plurality of alignment marks enter the visual field of analignment scope. For this reason, the necessity for identifying orspecifying a target alignment mark from a plurality of alignment marksin the visual field is increasing.

SUMMARY OF THE INVENTION

The present invention has been made in consideration of the abovesituation, and has as its object to obtain a position of a target markfrom an image of an object including a plurality of marks.

According to the first aspect of the present invention, there isprovided an apparatus which detects a position of a mark included in anobject. The apparatus comprises a unit which senses an image of theobject, wherein a plurality of marks included in the object can beincluded in the image, a unit which extracts a feature of a region,other than a region of a target mark of the plurality of marks, of theimage sensed by the sensing unit, and a unit which calculates a positionof the target mark based on the feature extracted by the extractingunit.

In the preferred embodiment of the present invention, the feature maycorrespond to an auxiliary mark, included in the object, associated withone of the plurality of marks. The auxiliary mark can be connected toone of the plurality of marks. The auxiliary mark can be associated withthe target mark or one of the plurality of marks other than the targetmark.

In the preferred embodiment, the feature may correspond to relativepositions of some of the plurality of marks or a position of one of theplurality of marks, of which a position relative to the target mark isknown.

In the preferred embodiment, the object may include a substrate on whicha device is to be formed.

In the preferred embodiment, the apparatus can further comprise a stageunit which positions the substrate. In such an application, theapparatus can further comprise a unit which controls positioning of thesubstrate by the stage unit based on the position of the target markcalculated by the calculating unit.

According to the second aspect of the present invention, there isprovided an apparatus which exposes a substrate to radiant energy. Theapparatus comprises a stage unit which positions the substrate, a unitwhich senses an image of the substrate, wherein a plurality of marksincluded in the substrate can be included in the image, a unit whichextracts a feature of a region, other than a region of a target mark ofthe plurality of marks, of the image sensed by the sensing unit, a unitwhich calculates a position of the target mark based on the featureextracted by the extracting unit, and a unit which controls positioningof the substrate by the stage unit based on the position of the targetmark calculated by the calculating unit.

According to the third aspect of the present invention, there isprovided an apparatus which exposes a substrate to radiant energy. Theapparatus comprises a unit which projects a pattern of radiant energy tothe substrate, a unit which holds a mask having an auxiliary pattern, tobe projected by the projecting unit, for identifying a target markformed on the substrate, and a unit which controls an operation ofprojecting the auxiliary pattern by the projecting unit.

According to the fourth aspect of the present invention, there isprovided a substrate comprising a region for a chip and a plurality ofmarks formed such that a position of a target mark of the plurality ofmarks is recognized.

According to the fifth aspect of the present invention, there isprovided a method of detecting a position of a mark included in anobject. The method comprises steps of sensing an image of the object,wherein a plurality of marks included in the object can be included inthe image, extracting a feature of a region, other than a region of atarget mark of the plurality of marks, of the image sensed in thesensing step, and calculating a position of the target mark based on thefeature extracted in the extracting step.

According to the sixth aspect of the present invention, there isprovided a method of manufacturing a device, the method comprising stepsof sensing an image of a substrate, wherein a plurality of marksincluded in the substrate can be included in the image, extracting afeature of a region, other than a region of a target mark of theplurality of marks, of the image sensed in the sensing step, calculatinga position of the target mark based on the feature extracted in theextracting step, and transferring a pattern concerning the device to thesubstrate based on the position of the target mark calculated in thecalculating step.

Other features and advantages of the present invention will be apparentfrom the following description taken in conjunction with theaccompanying drawings, in which like reference characters designate thesame or similar parts throughout the figures thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate embodiments of the invention and,together with the description, serve to explain the principles of theinvention.

FIG. 1 is a view schematically showing the arrangement of a lithographysystem (exposure apparatus) according to a preferred embodiment of thepresent invention;

FIG. 2A is a view showing an example of a group of alignment marksobserved in a low-magnification visual field;

FIG. 2B is a view for explaining auxiliary patterns used to identify atarget alignment mark;

FIG. 2C is a view showing an example of auxiliary patterns;

FIG. 2D is a view showing another example of auxiliary patterns;

FIG. 2E is a view showing still another example of auxiliary patterns;

FIG. 3A is a view showing an example of a group of alignment markspartially observed in a low-magnification visual field;

FIG. 3B is a view for explaining a change of a search range;

FIG. 3C is a view showing an example of a layout of alignment marks;

FIG. 3D is a view showing another example of a layout of alignmentmarks;

FIG. 3E is a view showing an example of a group of alignment markspartially observed in a low-magnification visual field;

FIG. 4 is a view showing a shot region and global alignment marks on awafer;

FIG. 5A is a view schematically showing the arrangement of a lithographysystem (exposure apparatus) according to another preferred embodiment ofthe present invention, which has an auxiliary pattern transfer function;

FIG. 5B is a view for explaining the auxiliary pattern transferfunction;

FIG. 5C is a view for explaining the auxiliary pattern transferfunction;

FIG. 6 is a flow chart for explaining the procedure of global alignmentin the lithography system or exposure apparatus according to thepreferred embodiment of the present invention;

FIG. 7 is a flow chart for explaining the procedure of global alignmentin the lithography system or exposure apparatus according to thepreferred embodiment of the present invention;

FIG. 8A is a view showing an arrangement example of an alignment mark;

FIG. 8B is a view schematically showing a situation in which analignment mark is moved into the visual field of a high-magnificationsensor;

FIG. 8C is a view showing a group of alignment marks in the visual fieldof a low-magnification sensor;

FIG. 9 is a flow chart showing the flow of the entire manufacturingprocess of a semiconductor device; and

FIG. 10 is a flow chart showing the flow of the entire manufacturingprocess of a semiconductor device.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will be described belowwith reference to the accompanying drawings.

[First Embodiment]

An example of an alignment mark (position detection mark) to be used inthe global alignment in a lithography system or an exposure apparatusaccording to a preferred embodiment of the present invention will bedescribed first with reference to FIG. 8A. An alignment mark FXY of thisembodiment is designed to make it possible to simultaneously executemeasurement in the X direction and that in the Y direction in globalalignment.

In global alignment, a mark FX for X-direction measurement in a window Xshown in FIG. 8A is observed with a high-magnification scope(high-magnification detection system or high-magnification observationsystem). Simultaneously, a mark FY for Y-direction measurement in awindow Y is observed with a high-magnification scope. With thisoperation, the X- and Y-direction positions (coordinates) of thealignment mark FXY are detected at a high resolution.

Global alignment according to the preferred embodiment of the presentinvention will be described next with reference to FIGS. 1 and 4. When awafer is supplied to a lithography system shown in FIG. 1 by a transfermechanism (not shown), a mechanical alignment apparatus MA determinesthe coarse petition of the wafer on the basis of the peripheral positionof the wafer and the position of a direction specifying portion (N inFIG. 4), called an orientation flat or notch.

Next, the wafer is placed on a chuck CH mounted on a wafer stage STG bya wafer supply apparatus (not shown). After that, global alignment isperformed to accurately obtain the position of the wafer W and theposition of each exposure shot. In the global alignment according tothis embodiment, X-direction measurement marks FX1 to FX4 andY-direction measurement marks FY1 to FY4 in a plurality of globalalignment marks FXY1 to FXY4 on the wafer W are measured using ahigh-magnification scope (high-magnification detection system orhigh-magnification observation system), thereby obtaining the X- andY-direction shifts and rotation component of the wafer W from thereference position and the magnification component of the shot array.

An alignment scope which can observe the alignment mark FXY shown inFIG. 8A simultaneously with a low-magnification system andhigh-magnification system will be described next. A microscope for waferalignment, i.e., an alignment scope SC shown in FIG. 1 is designed tomake it possible to observe an alignment mark simultaneously with alow-magnification system and high-magnification system to detect theposition of the alignment mark.

Alignment mark illumination light is guided from an alignment markillumination light source Li into the scope SC, passes through a halfmirror M1 (or a polarizing beam splitter), and illuminates an alignmentmark (e.g., the mark FXY1 shown in FIG. 4) on the wafer W. Reflectedlight from the wafer W passes through the half mirror M1 and a halfmirror M2 and reaches a high-magnification detection sensor (e.g., aphotoelectric conversion element) S2. Simultaneously, the reflectedlight from the wafer W also passes through the half mirrors M1 and M2and reaches a low-magnification detection sensor (e.g., a photoelectricconversion element) S1. Images sensed by the sensors S1 and S2 aresupplied to a processing apparatus P. The processing apparatus Pexecutes a predetermined process to calculate the position of thealignment mark.

Calculation of the alignment mark position is done for each of the twosensors S1 and S2 of the low- and high-magnification systems. Anelectrical signal (image signal.) photoelectrically converted by thelow-magnification system detection sensor S1 is converted from an analogsignal into a digital signal by an A/D converter AD1 and then stored inan image memory MEM1 as image data. An arithmetic device COM1 searchesfor the alignment mark FXY (FX and FY) while executing a patternmatching process or the like for the image data in the image memoryMEM1.

A template for pattern matching can be constituted by a two-dimensionalpattern formed from, e.g., eight vertical lines and eight horizontallines, as shown in FIG. 2B by example. The matching process algorithm oftemplate matching is designed such that not only a mark that strictlyhas the same shape as that of the template but also a mark whose linewidth or the like is different from that of a standard mark can bedetected. More specifically, the mark detection algorithm allowsdetection of all marks even when a mark which has a shape similar tothat of the template (shape with a common feature portion to bedetected), although its structure such as a line width or mark step isdifferent, is present in the image stored in the image memory MEM1,i.e., in the low-magnification visual field as well as marks having thesame shape as that of the template.

In addition, when two templates are prepared, marks that are classifiedinto two types, e.g., a mark having eight vertical lines and eighthorizontal lines, as shown in FIG. 2B as a characteristic feature, and amark (not shown) having six vertical lines and six horizontal lines as acharacteristic feature can be detected. Furthermore, when a plurality oftemplates are prepared, marks that are classified into types equal innumber to the templates can be detected.

To detect alignment marks, various methods except template matching andpattern matching can also be applied.

The reflected light for the high-magnification system can be madedifferent from that for the low-magnification system by using the commonillumination light source Li and adjusting the accumulation times in thesensors S1 and S2.

The principle of mark observation performed using the high-magnificationsystem (M1, M2, and S2) and low-magnification system (M1 and S1)simultaneously will be described next with reference to FIGS. 8A and 8B.FIG. 8A illustrates an observable visual field HF of thehigh-magnification system (M1, M2, and S2). For both the X-directionpattern FX and the Y-direction pattern FY, shifts with respect to thewindows X and Y are hardly allowed.

FIG. 8B illustrates an observable visual field MF of thelow-magnification system (M1 and S1). The visual field MF of thelow-magnification system is wider than the visual field HF of thehigh-magnification system. The arithmetic device COM1 calculates smallmoving amounts dx and dy of the wafer W which should be moved to put analignment mark P1 to be detected into the visual field HF of thehigh-magnification system on the basis of the alignment mark observationresult (the position of the alignment mark to be detected) by thelow-magnification system (M1 and S1) while observing the alignment marksimultaneously with the high-magnification system and low-magnificationsystem.

High-speed wafer alignment using the alignment marks shown in FIGS. 2Aand 2B and the alignment scope SC shown in FIG. 1 will be described nextas the preferred embodiment of the present invention. The lightcomponent that has passed through the half mirror M2 is guided to thesensor S2 of the high-magnification system and forms the image of thealignment mark FXY on the image sensing surface of the sensor S2. Inaddition, the light component reflected by the half mirror M2 is guidedto the sensor S1 of the low-magnification system and forms the image ofthe alignment mark FXY on the image sensing surface of the photoelectricconversion element S1.

It is preferable to simultaneously form the images of the alignment markFXY and simultaneously observe the alignment mark FXY. The reason forthis will be described below. If the shift amounts dx and dy shown inFIG. 8B, which are obtained by the low-magnification system, fall withinan allowable range, the image of the alignment mark FXY that allowsaccurate position measurement is formed on the high-magnification systemsensor S2. Hence, the position detection result for the alignment markFXY using the high-magnification system sensor S2 is valid.

The allowable range means, in the example shown in FIG. 8A, shiftamounts with which it is determined that the pattern FX (pattern formedfrom eight lines) in the X direction and the pattern FY (pattern formedfrom eight lines) in the Y direction are present within the windows Xand Y, respectively. Hence, when the shift amounts dx and dy obtained bythe low-magnification system fall within the allowable range, anaccurate detection result (mark position) in the high-magnificationsystem can be obtained as quickly as possible. Conversely, when theshift amounts dx and dy obtained by the low-magnification system falloutside the allowable range, the stage STG is finely moved by dx and dy.After that, the mark position is detected again by thehigh-magnification system.

A mark identification method to be used when a plurality of alignmentmarks having identical or similar shapes (shapes with a common featureportion to be detected) are present in the visual field MF of thelow-magnification system will be described next with reference to FIG.2A. A description will be made below assuming that the alignment mark(i.e., the target alignment mark) to be detected in the currentlithography step (current exposure step) is P1.

When alignment was executed even in the preceding lithography stepbefore the current lithography step (e.g., when the current exposurestep is the exposure step of a second or subsequent time), for example,alignment marks L1, M1, NI, and O1 that were formed and used in thepreceding step and have the same shape as that of the alignment mark P1may be laid out adjacent to the current target alignment mark P1.Alternatively, the alignment marks L1, M1, NI, O1, and P1 may be markswhich have similar shapes (i.e., shapes with a common feature portion tobe detected), but different line widths and three-dimensional patternsfor the purpose of optimizing the alignment mark structure.

In this embodiment, to detect only the current target alignment mark P1from the visual field MF of the low-magnification system and to obtainthe shift amounts dx and dy (moving amounts for observation with thehigh-magnification system), some or all of auxiliary patterns CPa, CPb,CPC, and CPd or no auxiliary patterns are added to regions that do notinfluence the measurement of the alignment mark FXY at a highmagnification, as shown in FIG. 2B, thereby identifying the targetalignment mark. For example, no auxiliary pattern is added to thealignment mark P1 while a small square is added to the upper rightportion of the alignment mark O1.

In this way, auxiliary patterns are added to regions that do notinfluence high-magnification measurement in the formation regions of thealignment marks L1, M1, N1, O1, and P1 to identify the alignment marksL1, M1, N1, O1, and P1. An auxiliary pattern is preferably formed in aregion outside a chip region where a device pattern (e.g., a circuitpattern) is formed and, typically, between chip regions.

The target alignment mark can also be identified on the basis of thepositional relationship relative to a feature portion (e.g., a portionhaving an extractable feature) of a device pattern. In this case,however, a pattern that is much more complex than an alignment mark mustgenerally be detected as an auxiliary pattern, resulting in a higharithmetic process load.

In this case, the auxiliary pattern is inevitably part of the pattern ofthe device to be manufactured. Hence, the template to be used todetermine the target alignment mark depends on the pattern of eachdevice to be manufactured.

Furthermore, in this case, no auxiliary pattern can be determined if,for example, device patterns around a group of alignment marks areuniform patterns having no feature portion or periodical patterns. Thatis, to use a pattern in a chip region as an auxiliary pattern is greatlyrestricted and is therefore undesirable.

Hence, as described above, an auxiliary pattern is preferably formed onpurpose (i.e., the auxiliary pattern is not inevitably formed as apattern in a chip region but formed mainly for the purpose ofidentifying an alignment mark) in a region outside a chip region (i.e.,a region where formation of a mark or pattern for position detection isallowed).

A method of discriminately a plurality of alignment marks usingauxiliary patterns will be described next with to FIGS. 2A and 2B. Whenalignment marks in the state as shown in FIG. 2A are present in thevisual field MF of the low-magnification system (M1 and S1), thepositions of the five alignment marks are detected by the arithmeticdevice COM1 for the low magnification. A control apparatus MC determinesthe presence/absence of the auxiliary patterns CPa, CPb, CPc, and CPdshown in FIG. 2B for each of the five detected positions.

The presence/absence of an auxiliary pattern can be determined by amethod of, e.g., executing template matching or analyzing a contrastchange using a histogram or the like for each of the regions (in thisembodiment, the four corners of a rectangular region defined foralignment mark formation) where auxiliary patterns are to be formed.

The auxiliary patterns may be separated from a center C of the alignmentmark equidistantly or by different distances. In the example shown inFIG. 2B, the center C is assumed to be the origin (reference position).The coordinates of the auxiliary pattern CPa are defined as (Xa,Ya). Thecoordinates of the auxiliary pattern CPb are defined as (-Xb,Yb). Thecoordinates of the auxiliary pattern CPc are defined as (Xc, -Yc). Thecoordinates of the auxiliary pattern CPd are defined as (-Xd, -Yd). Suchpieces of coordinate information are loaded to the internal memory ofthe control apparatus MC before the exposure process.

In this example, each auxiliary pattern is square. However, an auxiliarypattern need not always have the square shape and may have another shape(for example, a rectangle, circle, polygon, pattern, number, symbol,character, or the like, may be used). As far as the auxiliary patternscan be observed in the visual field MF of the sensor S1, the distancebetween the alignment mark and each auxiliary pattern is notparticularly limited, i.e., they may be close to or apart from eachother.

The control apparatus MC loads information shown in Table 1 below to theinternal memory (e.g., a RAM) as well as the coordinate informationbefore the exposure process. The target alignment mark (P1 in thisexample) can be discriminated on the basis of the information.

TABLE 1 CPa CPb CPc CPd L1 present present absent absent M1 absentpresent absent absent N1 absent present present absent O1 present absentabsent absent P1 absent absent absent absent

To identify the target alignment mark P1, an alignment mark whosecombination of auxiliary patterns matches the combination assigned to P1in Table 1 is searched for from the five alignment marks. When thetarget alignment mark is discriminated on the basis of thepresence/absence of auxiliary patterns at the four portions, as in thisexample, the target alignment mark can be discriminated from 16alignment marks at a maximum.

The procedure of global alignment in the lithography system or exposureapparatus according to the preferred embodiment of the present inventionwill be described next with reference to FIGS. 6 and 7. The processshown in the flow charts in FIGS. 6 and 7 is controlled by the controlapparatus MC.

The schematic procedure of global alignment is indicated by steps S101to S107 in FIG. 6.

First, in step S101, the control apparatus MC outputs a command to astage control apparatus STC to cause it to move the wafer stage STG suchthat the alignment mark FXY1 shown in FIG. 4 enters the visual field ofthe alignment scope SC. Typically, the stage control apparatus STC movesthe stage STG to the target position in consideration of the positioninformation of the stage STG, which is supplied from a stage positionmeasuring apparatus (e.g., a laser interferometer) LP.

Each of the alignment marks FXY1 to FXY4 shown in FIG. 4 is designed tohave the pattern shown in FIG. 8A. As shown in FIG. 2A (not illustratedin FIG. 4), one or a plurality of alignment marks (L1, M1, N1, and O1 inFIG. 2A) whose feature portions to be detected are common to those ofthe target alignment marks FXY1 to FXY4 (P1 in FIG. 2A) in the currentglobal alignment are present around the target alignment marks.

In step S102, the control apparatus MC outputs commands to theprocessing apparatus P, alignment scope SC, and illumination lightsource Li to cause them to detect the positions of the marks FX1 and FY1(i.e., the X- and Y-direction positions of the alignment mark) byobserving the marks FX1 and FY1 (corresponding to the marks FX and FY inFIG. 8A) of the alignment mark FXY1. The detection result is sent fromthe processing apparatus P to the control apparatus MC.

The process procedure in step S102 (and step S104 to be described later)will now be described in detail with reference to the flow chart shownin FIG. 7. A description will be made here assuming that thehigh-magnification sensor S2 comprises an X-measurementhigh-magnification sensor for position measurement in the X directionand a Y-measurement high-magnification sensor for position measurementin the Y direction. In this case, each of the X-measurementhigh-magnification sensor and Y-measurement high-magnification sensorcan include, e.g., a line sensor. The high-magnification sensor S2 mayinclude an area sensor which simultaneously senses the mark FX 1 (FX)for the X-direction measurement and the mark FY1 (FY) for theY-direction measurement.

In this embodiment, high-magnification image sensing of the mark FX1(FX) for the X-direction measurement (step S110) and high-magnificationimage sensing of the mark FY1 (FY) for the Y-direction measurement (stepS111) by the high-magnification sensor S2 and low-magnification imagesensing by the low-magnification sensor S1 (S112) are simultaneouslyexecuted. These image sensing operations need not always be executedsimultaneously. However, when these operations are executedsimultaneously, the total process time can be shortened.

In addition, in this embodiment, position calculation of the mark FX(step S113) and position calculation of the mark FY (step S114) at thehigh magnification and position calculation of the target alignment markFXY1 (FX in FIG. 8A) and the remaining alignment marks and auxiliarypatterns at the low magnification (step S115) are executed in parallel.The position calculation of the marks FX and FY at the highmagnification is executed by an arithmetic device COM2. The positioncalculation of the alignment mark FXY1 at the low magnification isexecuted by the arithmetic device COM1.

An image sensed at a high magnification may not include the image of thetarget alignment mark FXY1. In this case, an erroneous position(coordinates) is calculated as the position of the target alignment markor the position calculation itself is impossible in steps S113 and S114.An example of the cause of such a position detection error ismisalignment by the mechanical alignment apparatus MA. On the otherhand, the visual field MF of the low-magnification system is designed toallow such an error. Hence, the target alignment mark can be sensed.

In step S115, the X- and Y-direction positions are calculated for all ofthe alignment marks L1, M1, N1, O1, and P1 (the target alignment mark isP1) and auxiliary patterns CPa, CPb, CPc, and CPd in the visual field MFof the low-magnification system (M1 and S1).

In step S116 next to step S115, the control apparatus MC identifies thetarget alignment mark P1 from the plurality of alignment marks on thebasis of the calculation result in step S115 and the information shownin Table 1 (information loaded to the control apparatus MC in advance).

In step S117 next to step S116, the control apparatus MC calculates themoving amounts (shift amounts for fine measurement) dx and dy of thewafer W to move the target alignment mark P1 into the visual field HF ofthe high-magnification sensor S2, as shown in FIG. 8B.

In step S118, the control apparatus MC determines whether the movingamounts dx and dy calculated in step S117 fall within the allowablerange. The allowable range means the range of positional shift amountsin which the position of the target alignment mark P1 can be detectedusing the high-magnification sensor S2 without moving the wafer W.

If it is determined that the moving amounts dx and dy fall within theallowable range, the control apparatus MC advances the process to stepS124 to determine the position of the mark FX1 and the position of themark FY1, which are calculated in steps S113 and S114, as the X- andY-direction positions of the target alignment mark FXY1 (P1). Then, theflow advances to step S103 (returns to the main routine).

If it is determined that the moving amounts dx and dy fall outside theallowable range, the control apparatus MC outputs a command to the stagecontrol apparatus STC in step S119 to cause it to finely move the waferstage STG (i.e., the wafer W) to correct the shift amounts dx and dy.With this operation, of the plurality of alignment marks, the targetalignment mark P1 enters the visual field of the high-magnificationsensor S2.

Next, in steps S120 and S121, the control apparatus MC executes,preferably simultaneously, high-magnification image sensing of the markFX1 (FX) for measurement in the X direction and high-magnification imagesensing of the mark FY1 (FY) for measurement in the Y direction.

Next, in step S122 and S123, the control apparatus MC executes positioncalculation of the mark FX and position calculation of the mark FY inparallel. With this process, the X- and Y-direction positions of thetarget alignment mark FXY1 are accurately calculated (detected).

As described above, in this embodiment, the alignment scope SC that isdesigned to simultaneously sense alignment marks at high and lowmagnifications is arranged. With the alignment scope SC, image sensingoperations at high and low magnifications are preferably simultaneouslyexecuted while keeping the wafer W stopped. The position of an alignmentmark (it is unknown whether the alignment mark is the target alignmentmark) is detected on the basis of the image sensing result at the highmagnification. In addition, the target alignment mark is identified, andits position (and positional shift amount) is detected on the basis ofthe image sensing result at the low magnification.

It is determined on the basis of the position of the target alignmentmark whether the alignment mark whose position is detected at the highmagnification is the target alignment mark. If the alignment mark whoseposition is detected at the high magnification is the target alignmentmark, the position detection result at the high magnification is used asthe position detection result of the target alignment mark. Otherwise,the wafer W is moved to a position at which the identified targetalignment mark can be observed at the high magnification, and theposition of the target alignment mark is detected at the highmagnification.

If the target alignment mark is within the visual field HF of thehigh-magnification sensor S2 from the beginning, and the position of thetarget alignment mark is detected from the beginning, the position ofthe target alignment mark can be detected by one position detectionoperation. Hence, according to this embodiment, the speed of globalalignment can be increased.

Referring back to FIG. 6, after the position of the alignment mark FXY1is calculated in step S102, the control apparatus MC outputs a commandto the stage control apparatus STC to cause it to move the wafer stageSTG such that the alignment mark FXY2 shown in FIG. 4 enters the visualfield of the alignment scope SC. The control apparatus MC executes thesame process as in step S102 (FIG. 7) for the alignment mark FXY2,thereby calculating the X- and Y-direction positions of the alignmentmark FXY2.

When the positions of the two alignment marks FXY1 and FXY2 aredetected, the position of the wafer W on the chuck CH can roughly beobtained. In this embodiment, target positions to be used to move theremaining alignment marks FXY3 (FX3 and FY3) and FXY4 (FX4 and FY4) intothe visual field HF of the high-magnification sensor S2 are calculatedon the basis of the position detection results of the alignments marksFXY1 and FXY2.

The target positions of the alignment marks FXY3 (FX3 and FY3) and FXY4(FX4 and FY4) can be calculated in the following way. First, anX-direction shift amount (ShiftX), a Y-direction shift amount (ShiftY),rotation component θ, and a wafer magnification component Mag areobtained on the basis of the X- and Y-direction positions of the twoalignments marks FXY1 and FXY2. The amounts ShiftX, ShiftY, and θ areshift amounts when the wafer W is placed on the chuck CH, and correspondto the offset of mechanical alignment. The amount Mag is the extensionamount of the shot pattern on the wafer W.

If these amounts are large, even when the third and fourth alignmentmarks FXY3 and FXY4 are moved to the position immediately under thealignment scope SC on the basis of their designed positions, they cannotenter the visual field of the high-magnification system (M1, M2, and S2)of the alignment scope SC.

To prevent this, the shift between the shot layout of the wafer and thestage coordinate system is calculated on the basis of the amounts θ,Mag, ShiftX, and ShiftY. More specifically, a small correction amount tobe used to align the grid on the wafer W to the grid of the wafer stageSTG is obtained. When the target positions of the alignment marks FXY3(FX3 and FY3) and FXY4 (FX4 and FY4) are corrected in accordance withthe fine correction amount, the alignment marks FXY3 (FX3 and FY3) andFXY4 (FX4 and FY4) can be moved into the visual field HF of thehigh-magnification sensor S2 without using the low-magnification sensorS1.

When the θ component is corrected (for example, the wafer W is rotatedby the chuck CH or stage STG), the third and fourth alignment marks FXY3and FXY4 can be observed without any shift of the θ component. In thiscase, however, since a rotation operation is necessary, the totalprocess time becomes long. From the viewpoint of process time, it isadvantageous to omit correction of the θ component.

In step S106 next to step S105, the control apparatus MC moves thealignment mark FXY3 (FX3 and FY3) to the position immediately under thealignment scope SC in accordance with the corrected target position anddetects the position of the alignment mark FXY3 using thehigh-magnification sensor S2. In step S107, the control apparatus MCmoves the alignment mark FXY4 (FX4 and FY4) to the position immediatelyunder the alignment scope SC in accordance with the corrected targetposition and detects the position of the alignment mark FXY4 using thehigh-magnification sensor S2. Thus, the global alignment is ended.

The arrangement example shown in FIG. 1 indicates a lithography systemor exposure apparatus of an off-axis alignment scheme. However, whenalignment marks can be simultaneously observed as low and highmagnifications, any other alignment scheme can be employed. Morespecifically, the present invention can also be applied to, e.g., a TTLalignment scheme for observing an alignment mark through a projectingoptical system LENS or a TTR alignment scheme for observing an alignmentmark through a reticle R.

The number of alignment marks to be detected in global alignment and thenumber of alignment marks that can enter the visual field of thelow-magnification system are not particularly limited.

In addition, the method of identifying a target alignment mark from aplurality of alignment marks in the visual field is preferably appliedto the above lithography system or exposure apparatus capable ofsimultaneous observation with the low-magnification system andhigh-magnification system. However, the present invention can also beapplied to a type of system which observes an alignment mark with thehigh-magnification system on the basis of an observation result from thelow-magnification system. More specifically, the present invention canalso be applied to a sequential process for observing alignment marksusing the low-magnification system to identify and position-detect atarget alignment mark (S112, S115, and S116), calculating the shiftamounts dx and dy (S117), moving the stage STG by dx and dy (S119), anddetecting the position of the target alignment mark P1 using thehigh-magnification system (S120, S121, and S122).

In this case, since the sequential process is executed, the timerequired for global alignment becomes long. However, even in aconventional hardware configuration incapable of simultaneousmeasurement at low and high magnifications, a target alignment mark canbe identified from a plurality of alignment marks present in the visualfield.

Auxiliary patterns to be used to identify alignment marks are notlimited to the example shown in FIG. 2B. Any shape and layout can beemployed as long as alignment marks can be identified. For example, asshown in FIG. 2C, auxiliary patterns (identification marks) differentbetween alignment marks may be used. As shown in FIG. 2D, auxiliarypatterns (identification marks) IP may be laid out outside regions DAdefined for formation of alignment marks. In this case, when thepositions of a plurality of alignment marks that are present in thelow-magnification visual field are calculated, and then, the shape ofthe auxiliary pattern IP having a predetermined positional relationshipfrom the position (e.g., the central position) of each alignment mark isdetected by image processing such as template matching using a templatefor each auxiliary pattern, the target alignment mark can be identified.

Furthermore, as shown in FIG. 2E, in the alignment mark FXY formed fromthe X-direction measurement mark FX and Y-direction measurement mark FY,each alignment mark is made to partially have a form different fromthose of the remaining alignment marks and deformed without generatingany influence, thereby identifying the alignment marks. In this case,the deformed portions (the projecting portions in the example shown inFIG. 2E) correspond to auxiliary patterns. As an identification method,various methods can be applied, including a method of measuring the sizesuch as the length of a corresponding portion.

[Second Embodiment]

Another embodiment which identifies a target alignment mark from aplurality of alignment marks in a single visual field will be described.The basic hardware configuration, alignment marks, and measurement floware the same as those of the first embodiment, and a description thereofwill be omitted. Only different points will be described.

As shown in FIG. 3A, when a target alignment mark P1 is located outsidea visual field MF of a low-magnification sensor S1, position detectionof the target alignment mark P1 is normally impossible. However, sincealignment marks L1, M1, and N1 other than the target alignment mark P1are present in the visual field MF, fine shift amounts dx and dy or theposition of the alignment mark P1 can be calculated in step S117 whenthe positional relationship between the alignment mark P1 and each ofthe alignment marks L1, M1, and N1 is known.

For example, assume that the alignment mark L1 can be identified inaccordance with its auxiliary pattern, and the position of the alignmentmark L1 can be detected. In this case, the X- and Y-direction relativedistances between the alignment mark L1 and the target alignment mark P1are kx and ky. When the alignment mark L1 detected within the visualfield MF is shifted from a visual field center FC by shift amounts MXand MY, the amounts dx and dy of the movement of a stage STG for finemeasurement using the high-magnification system are calculated bydx=MX+kx and dy=MY+ky, respectively.

As described above, even when the target alignment mark is not presentin the visual field, or the target alignment mark cannot be identified,as long as the alignment marks around the target alignment mark can beidentified, and their positions can be detected, the position of thetarget mark can be calculated on the basis of the known positionalrelationship between each alignment mark and the target mark. Hence, thetarget mark can be moved to a visual field HF of the high-magnificationsystem, and the position of the target mark can be detected at a highmagnification.

[Third Embodiment]

Still another embodiment which identifies a target alignment mark from aplurality of alignment marks in a single visual field will be described.The basic hardware configuration, alignment marks, and measurement floware the same as those of the first embodiment, and a description thereofwill be omitted. Only different points will be described.

Wafers are normally processed in blocks of lots. The lots are processedby a single manufacturing apparatus. When the reproducibility ofmechanical alignment is high, amounts ShiftX, ShiftY, and θ calculatedfor the first wafer are defined as the offset of mechanical alignment.The position of the second wafer is shifted in advance by the amountsShiftX, ShiftY, and θ. When this wafer is placed on a stage STG, theoffset error of mechanical alignment becomes close to 0.

Hence, even when a plurality of alignment marks are observed in a singlevisual field, the target alignment mark is sensed at the center of thevisual field. In this case, preferably, a search range SA in which analignment mark is to be searched for in a visual field MF is limitednear the center of the visual field MF so as not to search for anyalignment mark outside the search range SA. The search range SA is setto be larger than a high-magnification visual field HF and always allowsobservation of the target alignment mark within the allowable mechanicalalignment error. With this arrangement, the time required for imageprocessing for searching for a target mark is shortened.

If the mechanical alignment accuracy and reproducibility are high, andthe amounts ShiftX and ShiftY fall within the allowable range fordetection at a high magnification, target alignment mark positiondetection using the low-magnification system and wafer movement on thebasis of the detected position of the target alignment mark can beomitted, as a matter of course.

[Fourth Embodiment]

Still another embodiment which identifies a target alignment mark fromalignment marks in a single visual field will be described. In the firstto third embodiments, an auxiliary pattern is added to a targetalignment mark, and the target alignment mark is discriminated using theauxiliary pattern. The fourth embodiment provides a method ofdiscriminating a target alignment mark from a plurality of alignmentmarks present in a visual field without using any auxiliary pattern. Thebasic hardware configuration, alignment marks, and measurement flow arethe same as those of the first embodiment, and a description thereofwill be omitted. Only different points will be described.

In the example shown in FIG. 3C, a target alignment mark P1 and aplurality of alignment marks L1, M1, N1, and O1 are present in alow-magnification visual field MF. In the example shown in FIG. 3C, thepositions of the alignment marks are determined such that the alignmentmarks are separated from each other by different distances in the visualfield MF. More specifically, in the example shown in FIG. 3C, lengthsSPX1, SPX2, SPY1, and SPY2 are set to be different from each other.

For example, when the positions of two or more alignment marks can bedetected in the visual field MF, the alignment marks can be identifiedin step S116 on the basis of the relative positional relationshipbetween the alignment marks. Then, the position (and necessary movingamounts dx and dy) of the target alignment mark can be detected in stepS117 on the basis of the known positional relationship between thetarget alignment mark and the identified alignment marks.

As described above, when the position of the target alignment mark(e.g., P1) is detected, the moving amounts dx and dy necessary forobserving the target alignment mark at a high magnification can becalculated. By moving a stage STG in accordance with the moving amounts,the target alignment mark can be observed at a high magnification, andits position can be detected.

[Fifth Embodiment]

Still another embodiment which identifies a target mark from a pluralityof alignment marks in a single visual field will be described. In thefifth embodiment, a method of identifying a target alignment mark from aplurality of alignment marks that are present in a visual field withoutusing any auxiliary pattern and setting different distances between theplurality of alignment marks. The basic hardware configuration,alignment marks, and measurement flow are the same as those of the firstembodiment, and a description thereof will be omitted. Only differentpoints will be described.

In this embodiment, when all or some of the alignment marks L1, M1, N1,O1, P1, and Q1 are present in a visual field MF, as shown in FIG. 3D,the position of a target alignment mark is detected on the basis of thepositions and number of alignment marks detected in the visual field MF.A description will be given below assuming that the target alignmentmark in the alignment marks L1, M1, N1, O1, P1, and Q1 is P1.

First, a case wherein all the alignment marks L1, M1, N1, O1, P1, andQ1, including the target alignment mark P1, are present in the visualfield MF, as shown in FIG. 3D, will be examined. In this case, theposition of the target alignment mark P1 can be identified, and itsposition can be detected on the basis of the known position (the secondcolumn of the second row in this example) of the target alignment markP1 in the group of alignment marks L1, M1, N1, O1, P1, and Q1.

A method of estimating (determining) a target mark will be describedwith reference to FIG. 3E, including a case wherein only some of thealignment marks are detected in the visual field MF. A description willbe made assuming that the lower left apex of the visual field MF isdefined as the origin (0,0) of the coordinate system. In this case, thevisual field MF corresponds to the upper right quadrant of thecoordinate system.

Let Ax be the X-direction size of the visual field MF, Ay be theY-direction size, Mx be the X-direction interval between the alignmentmarks, and My be the Y-direction interval. Nx (number of columns) X Ny(number of rows) alignment marks are two-dimensionally laid out. Thefollowing conditions are satisfied.Ax>Mx*(Nx−1)Ay>My*(Ny−1)

The start alignment mark in the alignment mark group two-dimensionallylaid out is defined as the alignment mark at the lower left of thealignment mark group. The coordinates of the plurality of alignmentmarks detected in the visual field MF are defined as (Xij,Yij) {i=1, 2,. . . , k, j=1, 2, . . . , 1, k≦Nx, 1 ≦Ny}.

On the basis of the above definition, the method of determining theposition (coordinates) of the target mark and the moving amounts (shiftamounts) to the target mark will be described. As an example, a methodof identifying the target mark P1 on the basis of the number of detectedalignment marks in the Y direction (the number of alignment marks whosepositions can be detected in the visual field) will be described.

When the number of alignment marks that can be detected in the visualfield MF is l (<Ny), the upper or lower portion of the Ny alignmentmarks arrayed in the Y direction falls outside the visual field MF. Whenl =Ny, no alignment marks fall outside the visual field MF in the Ydirection.

First, the moving direction (upward or downward) of the alignment markgroup in the visual field MF is determined. This determination can bedone in accordance with, e.g., the following procedure. First, anaverage position in the Y direction is obtained for each detectedalignment mark. ${Meany} = {\frac{1}{k}{\sum\limits_{j = 1}^{k}y_{1y}}}$

Then, Meany is compared with the center of the visual field MF Ayc=Ay/2.If Meany>Ayc, it is determined that the alignment mark group has movedupward in the visual field MF. If Meany<Ayc, it is determined that thealignment mark group has moved downward in the visual field MF.

Next, the start coordinates of the alignment mark group are calculated.The start coordinates are defined as the coordinates of the alignmentmark at the lowermost position in the Y direction and leftmost positionin the X direction. When it is determined from the above comparisonresult that the alignment mark group has moved upward in the visualfield MF, a position Topy of the start alignment mark corresponds to analignment mark position Miny=Min(y_(1j) {j=1, 2, . . . , l}) which hasthe minimum y-coordinate value in the detected alignment mark positions.

On the other hand, if it is determined that the alignment mark group hasmoved downward in the visual field MF, the start alignment mark may falloutside the visual field MF. An alignment mark Maxy=Max(y_(1j) {j=1, 2,. . . , l}) which has the maximum y-coordinate value in the detectedalignment mark positions corresponds to the position of the alignmentmark at the upper left corner of the alignment mark group. Hence, acoordinate calculated by Maxy−My*(Ny−1) indicates the position of thestart alignment mark. For the Y direction as well, the position of thestart alignment mark is determined by the same calculation as describedabove. With this operation, the coordinates of the start alignment markat the lower left corner of the alignment mark group can be determined.

That is, the coordinates of the start alignment mark can be determinedin accordance with the following conditions.

If (Meanx≧Axc)Topx=Min(x _(i1) {i=1, 2, . . . , k})

If (Meanx<Axc)Topx=Max(x _(i1) {i=1, 2, . . . , k})−Mx*(Nx−1)

If (Meany≧Ayc)

 Topy=Min(y _(1j) {j=1, 2, . . . , l})

If (Meany<Ayc)Topy=Max(y _(1j) {j=1, 2, . . . , l})−My*(Ny−1)

Next, the target mark coordinates are estimated on the basis of thestart alignment mark coordinates (Topx,Topy). The relative distances(Tdx and Tdy) between the target alignment mark and the start alignmentmark are known. Hence, the positions of the target alignment markcoordinates (Tx,Ty) are calculated byTx=Topx+TdxTy=Topy+Tdy

Finally, the distance from the center of the visual field MF to thetarget alignment mark is obtained, and the moving amounts (dx and dy) ofthe stage STG necessary for observing the center of the target alignmentmark at the center of a visual field HF of the high-magnification systemare calculated in accordance withdx=Ax/2−Txdy=Ay/2−Ty

Even in an extreme case wherein only one alignment mark is detected inthe visual field MF, the moving direction of the alignment mark groupcan be determined, and the coordinates of the target alignment mark thatis not present in the visual field MF and the necessary stage movingamounts can be determined. As a matter of course, even when thepositions of all alignment marks are detected, the coordinates of thetarget alignment mark and the necessary stage moving amounts can bedetermined in accordance with the above procedure.

The example shown in FIG. 3E will be described in detail. In the exampleshown in FIG. 3E, Nx=2 and Ny=3. The group of six alignment marks hasmoved to the lower right side in the visual field MF. The positions ofthe alignment marks L1 and O1 can be detected. The target alignment markis P1. When the average values Meanx and Meany of the coordinates of thedetected alignment marks are compared with the visual field center(Axc,Ayc), Meanx>Axc and Meany<Ayc.

Since Meanx>Axc, the minimum value Minx of the x-coordinate of thedetected alignment mark is selected, and Topx=Minx.

In addition, since Meany<Ayc, the maximum value of the y-coordinate ofthe detected alignment mark is selected, and Topy=Maxy−My*(3−1).

Since the distances Tdx and Tdy between the target alignment mark P1 andthe start alignment mark in the group of the six alignment marks areknown, the coordinates (Tx,Ty) of the target alignment mark P1 can becalculated in accordance withTx=Topx+TdxTy=Topy+Tdy

Then, the moving distances necessary for moving the target alignmentmark P1 to the visual field center of the visual field MF (and visualfield HF) can be calculated bydx=Ax/2−Txdy=Ay/2−Ty

In this way, even in a case wherein the target mark cannot be specifiedin the visual field, when the total number of alignment marks and therelative position of the target alignment mark in the alignment markgroup are known on the basis of the positions and number of detectedalignment marks, the position of the target mark can be detected, andthe moving amounts dx and dy necessary for moving the stage STG fordetection at the high magnification can be calculated. When the stageSTG is moved in accordance with the moving amounts, the target alignmentmark can be moved into the visual field HF of the high-magnificationsystem, and the position of the target alignment mark can be detected atthe high magnification.

As described above, according to this embodiment, on the basis of thenumber and positions of alignment marks detected in the visual field MF(in consideration of the known relative position of the target alignmentmark in the group of alignment marks), in step S117, the position of thetarget alignment mark can be detected, the moving amounts dx and dynecessary for observation of the target alignment mark at a highmagnification can be calculated, and by moving the stage STG inaccordance with the moving amounts, the target alignment mark can beobserved at the high magnification, and its position can be detected.

[Sixth Embodiment]

An auxiliary pattern used to identify an alignment mark can be formed bytransferring a pattern formed on a reticle R onto a wafer. Thisembodiment provides a method of transferring an auxiliary pattern bymeans other than a reticle.

As shown in FIG. 2A, drawing alignment marks and auxiliary patterns onthe reticle R and exposing the alignment marks and auxiliary patterns toa wafer in each step of semiconductor manufacturing restrict the reticledesign. Hence, it is preferable to transfer auxiliary patterns onto awafer using the function of an exposure apparatus. In this case, themarks or patterns to be drawn on the reticle R are only alignment marks(and device patterns).

FIG. 5A is a view showing the schematic arrangement of an exposureapparatus according to the sixth embodiment of the present invention.The same reference numerals as in FIG. 1 denote the same constituentelements. An alignment scope SC, processing apparatus P, illuminationlight source Li, and mechanical alignment apparatus MA are notillustrated in FIG. 5A for the illustrative convenience.

When global alignment is ended, the exposure apparatus executesstep-and-scan exposure or step-and-repeat exposure to transfer thepattern on the reticle R onto a wafer W. At this time, several alignmentmarks FXY are also simultaneously transferred. After that, the exposureapparatus executes a step of adding auxiliary patterns into thedefinition regions of the alignment marks or around them.

Patterns LM, MM, NM, and OM for auxiliary pattern formation are formedin advance, as shown in FIG. 5B, on a reference plate PL placed on thesurface of the reticle R shown in FIG. 5A. When a masking blade MS isdriven, exposure light from an illumination system IL irradiates only aspecific region of the reference plate PL. A reticle stage RSTG on whichthe reticle R and reference plate PL are placed is driven by a linearmotor (not shown) such that a corresponding pattern on the referenceplate PL moves into the exposure region while the position of thereticle stage is accurately measured by a position detection apparatus(e.g., an interferometer). A wafer stage STG on which the wafer W isplaced moves the wafer W such that the position on the wafer W where analignment mark is to be formed matches the exposure region by theexposure light passing through the blade MS.

An example in which an alignment mark O1 shown in FIG. 2A and itsauxiliary pattern are to be formed will be described. First, inprojecting and exposing a device pattern, a pattern (this pattern isformed together with the device pattern) corresponding to the alignmentmark O1 is transferred onto the wafer W together with the devicepattern.

Next, the pattern OM on the reference plate PL, which is used to form anauxiliary pattern for identification of the alignment mark O1, istransferred to a predetermined position (in the definition region of thealignment mark O1 in this example) of the wafer W. At this time, theposition of the blade MS is controlled such that only the region OM ofthe reference plate PL is irradiated, as shown in FIG. 5C.

For auxiliary patterns for alignment marks L1, M1, N1, and P1 as well,the mask patterns LM, MM, and NM are transferred every time thecorresponding device patterns and the alignment marks L1, M1, N1, and P1are transferred.

Alternatively, instead of preparing mask patterns for a plurality ofkinds of auxiliary patterns on the reference plate PL, only one maskpattern for an auxiliary pattern may be prepared and transferred topositions CPa, CPb, CPc, and CPd shown in FIG. 2B using the center ofthe alignment marks as a reference. To do this, for example, the bladeMS is located such that only the region of the mask pattern OM shown inFIG. 5B is illuminated, and the position of the wafer stage STG iscontrolled such that the mask pattern OM is transferred to the positionsCPa, CPb, CPc, and CPd.

The shape of the mask pattern for an auxiliary pattern is not limited tothat shown in FIG. 5B. For example, the mask pattern may be designed totransfer an auxiliary pattern having a rectangular shape, cross shape,or number sign shape as shown in FIGS. 2C and 2D by example.Alternatively, for the mask pattern for an auxiliary pattern, part of analignment mark may be extended, and the extended portion may be used asan auxiliary pattern as shown in FIG. 2E by example.

The auxiliary pattern transfer operation can be controlled by setting ajob of the lithography system. Which type of auxiliary pattern should betransferred before, after, or at the time of exposure of an alignmentmark is set in the job. On the basis of this setting, the drivingpositions of the blade MS and wafer stage STG can be controlled by acontrol apparatus MC.

[Device Manufacturing Method]

A device manufacturing method will be described below as an applicationexample of the exposure apparatus according to the present inventiondescribed in accordance with the above embodiments by example.

FIG. 9 is a flow chart showing the entire flow of the semiconductordevice manufacturing process. In step 1 (circuit design), the circuit ofa semiconductor device is designed. In step 2 (mask preparation), a maskis prepared on the basis of the designed circuit pattern. On the otherhand, in step 3 (wafer manufacture), a wafer is manufactured using amaterial such as silicon.

In step 4 (wafer process), called a preprocess, an actual circuit isformed on the wafer by lithography using the above mask and wafer. Instep 5 (assembly), called a post-process, a semiconductor chip is formedfrom the wafer prepared in step 4. This step includes processes such asassembly (dicing and bonding) and packaging (chip encapsulation).

In step 6 (inspection), inspections including an operation check testand a durability test of the semiconductor device manufactured in step 5are performed. A semiconductor device is completed with these processesand shipped (step 7).

FIG. 10 shows the detailed flow of the wafer process. In step 11(oxidation), the surface of the wafer is oxidized. In step 12 (CVD), aninsulating film is formed on the wafer surface. In step 13 (electrodeformation), an electrode is formed on the wafer by deposition. In step14 (ion implantation), ions are implanted into the wafer. In step 15(resist process), a photosensitive material is applied to the wafer.

In step 16 (exposure), the circuit pattern (device pattern) istransferred onto the wafer by the above exposure apparatus. At thistime, an alignment mark (position detection mark) and auxiliary patternare transferred to a position between chip regions or to a scribing linetogether with the circuit pattern. The auxiliary pattern may betransferred to the wafer using an auxiliary pattern mask prepared in theexposure apparatus.

In step 17 (development), the exposed wafer is developed. In step 18(etching), portions other than the developed resist image are etched. Instep 19 (resist removal), any unnecessary resist remaining after etchingis removed. By repeating these steps, a multilayered structure ofcircuit patterns is formed on the wafer.

As described above, according to the preferred embodiments of thepresent invention, a target alignment mark can be identified from aplurality of alignment marks (position detection marks) and/or theposition of the target alignment mark can be detected. The targetalignment mark can be identified using, e.g., an auxiliary mark. Theauxiliary mark is preferably formed in a region where a mark or patternfor position detection can be formed, e.g., a region between chipregions. The auxiliary mark may be transferred to a wafer together witha device pattern and an alignment mark by, e.g., projecting a masteronto the wafer. Alternatively, the auxiliary mark may be transferred tothe wafer using a mask for the auxiliary pattern prepared in theexposure apparatus. According to the latter method, no auxiliary patternneed be formed when the master such as a mask or reticle is formed.Hence, the restriction at the time of master formation is reduced.

The target alignment mark can also be identified by separating theplurality of alignment marks by different distances and detecting thedistances between the alignment marks at the time of observation. Evenin a case wherein the target mark is located outside the visual field ofan observation apparatus such as an alignment scope, when any one of theplurality of alignment marks can be identified on the basis of thedistance between the alignment marks, and the position of the identifiedalignment mark can be detected, the position of the target alignmentmark whose position relative to the detected alignment mark position isknown can be detected.

The target alignment mark can also be identified on the basis of thelayout of the alignment marks to be observed. More specifically, theposition of the target alignment mark in the group is known. For thisreason, when the group can be observed, the target alignment mark can beidentified, and its position can be detected.

Alternatively, when the positions of alignment marks that are present inthe visual field of the observation system are detected, the position ofthe target alignment mark can be calculated on the basis of the numberof the detected position detection marks and their detection positionsin the visual field.

Such alignment mark identification methods can be applied not only toglobal alignment but also to die-by-die alignment.

In addition, when alignment marks are observed using the high- andlow-magnification systems simultaneously, and the observation result bythe low-magnification system indicates that the target alignment mark ispresent in the visual field of the high-magnification system in anobservable state, the first position detection result by thehigh-magnification system is preferably employed. Otherwise, preferably,the wafer or high-magnification system is moved on the basis of theobservation result by the low-magnification system to move the targetalignment mark into the visual field of the high-magnification system,and the position of the target alignment mark is detected at a highaccuracy. Accordingly, alignment such as global alignment can beexecuted at a high speed, and a high throughput can be achieved.

According to the present invention, for example, a target positiondetection mark can be identified from a plurality of position detectionmarks, or the position of a target position detection mark in aplurality of position detection marks can be calculated.

As many apparently widely different embodiments of the present inventioncan be made without departing from the spirit and scope thereof, it isto be understood that the invention is not limited to the specificembodiments thereof except as defined in the appended claims.

1. An apparatus for detecting a position of a target mark included in anobject, said apparatus comprising: a unit which senses an image of theobject, the object having a plurality of marks including the target markwith respect to each unit region of the object, the target mark beingused for specifying a position of a corresponding unit region, each ofthe plurality of marks comprising a first mark and a feature of a regionoutside of the first mark, the feature corresponding to a structurepreviously formed on the object for identifying a positionalrelationship between the first mark and the target mark; a unit whichextracts the first mark and the feature in an image sensed by saidsensing unit; and a unit which detects a position of the target markbased on a position of the first mark and the feature.
 2. An apparatusaccording to claim 1, wherein the feature corresponds to an auxiliarymark associated with the first mark.
 3. An apparatus according to claim2, wherein the plurality of the first marks have different auxiliarymarks, respectively.
 4. An apparatus according to claim 2, wherein theauxiliary mark is connected to the first mark.
 5. An apparatus accordingto claim 2, wherein the auxiliary mark is surrounded by the first mark.6. An apparatus according to claim 1, wherein the feature corresponds torelative positions of the plurality of the first marks.
 7. An apparatusaccording to claim 1, wherein the feature corresponds to a position ofthe first mark relative to the target mark.
 8. An apparatus according toclaim 1, wherein the object is a substrate on which a device is to beformed.
 9. An apparatus according to claim 8, further comprising a stageunit which positions the substrate.
 10. An apparatus according to claim9, further comprising a unit which controls positioning of the substrateby said stage unit based on the position of the target mark detected bysaid detecting unit.
 11. An apparatus for exposing a substrate toradiant energy, said apparatus comprising: a stage unit which positionsthe substrate; a unit which senses an image of the substrate, thesubstrate having a plurality of marks including a target mark withrespect to each unit region of the substrate, the target mark being usedfor specifying a position of a corresponding unit region, each of theplurality of marks comprising a first mark and a feature of a regionoutside of the first mark, the feature corresponding to a structurepreviously formed on the substrate for identifying a positionalrelationship between the first mark and the target mark; a unit whichextracts the first mark and the feature in an image sensed by saidsensing unit; a unit which detects a position of the target mark basedon a position of the first mark and the feature; and a unit whichcontrols said stage unit so as to position the substrate based on theposition of the target mark.
 12. A method of detecting a position of atarget mark included in an object, said method comprising steps of:sensing an image of the object, the object having a plurality of marksincluding the target mark with respect to each unit region of theobject, the target mark being used for specifying a position of acorresponding unit region, each of the plurality of marks comprising afirst mark and a feature of a region outside of the first mark, thefeature corresponding to a structure previously formed on the object foridentifying a positional relationship between the first mark and thetarget mark; extracting the first mark and the feature in an imagesensed in said sensing step; and detecting a position of the target markbased on a position of the first mark and the feature.
 13. A method ofmanufacturing a device, said method comprising steps of: sensing animage of a substrate;, the substrate having a plurality of marksincluding a target mark with respect to each unit region of thesubstrate, the target mark being used for specifying a position of acorresponding unit region, each of the plurality of marks comprising afirst mark and a feature of a region outside of the first mark, thefeature corresponding to a structure previously formed on the substratefor identifying a positional relationship between the first mark and thetarget mark; extracting the first mark and the feature in an imagesensed in said sensing step; detecting a position of the target markbased on a position of the first mark and the feature; and transferringa pattern concerning the device to the substrate based on the positionof the target mark.